WADHURST ASTRONOMICAL SOCIETY

JUNE NEWSLETTER 2008

INDEX: MEETINGS, OTHER NEWS, CONTACTS

MEETINGS

MAY MEETING  

The meeting was introduced by Phil Berry who referred to our forthcoming visit to Greenwich and the Great Transit Circle with Gilbert Satterthwaite.  The proposed itinerary and notes are included later in the Newsletter.

Occultations

Talk given by Brian Mills

On occasions we have a truly practical demonstration of the skills of the amateur astronomer, and this was one of them.  Brian Mills is one of our own members and is well known to members through his monthly Sky Notes that appear in the WAS Newsletter.

He explained that because celestial bodies lie at different distances, their own motion makes it likely that at some stage one body will pass in front of another.

Brian defined a Transit as a smaller body passing across the disk of a larger one such as Venus transiting in front of the Sun as it will on June the 6th, 2012 during sunrise.

Then he spoke of Solar and Lunar Eclipses.

Very rarely a planet will obscure another planet, but this last happened in January 1818 and the next one will take place in November 2065, both involving Venus occulting Jupiter!

Asteroidal occultations occur quite frequently around the world.  In fact 18 occurred yesterday (20th May) and 20 tomorrow (22nd May) but the observer's position is very critical.  They can last something like 6/10th of a second.

Occultations can even occur when a local star with a big enough proper motion passes in front of a distant star.

In passing, Brian referred to BOSS - Big Occultation Steerable Satellite - planned to detect planets around stars by positioning a large lightweight sheet (70m square) to occult 99.998% light from a star that would allow a planet to be seen 1/10th arc-second away from the star.

Lunar occultations of the planets are not that rare.  In 2007, Uranus and Saturn were both occulted twice and Venus, once.  This year Mars, Neptune and Venus are occulted as seen from Greenwich.

We were shown an image Brian had taken last year from his observatory in Hildenborough using a Meade and Toucam.  The contrast was very great but Saturn could be seen remarkably clearly.

We were shown an image taken from the Ascension Island in the South Pacific in April 1998 of a double planetary occultation.  In this extraordinary image we could see Venus on the limb of the moon and Jupiter further round.  It was even possible to see Ganymede and Io.

Observations of the occultation of Saturn's Titan gave astronomers important data of its atmosphere.

The Occultations Brian wanted to talk about mainly were lunar occultations of stars.

The Moon travels in a band close to the ecliptic, the plane of the Earth's orbit around the Sun.  The Moon can vary by up to about 7 degrees from the ecliptic.  Brian showed this band from the well-known Norton's Star Atlas.  (Norton had been a teacher at Judd School in Tonbridge)

There are some 850 naked eye stars in this band, which includes Antares, Aldebaren, Regulus and Spica.

First, the observer needs predictions on when occultations are going to occur.  A good source is the British Astronomical Association Annual Handbook, listing events down to magnitude 7.5.  Brian also uses further predictions from the Society for Popular Astronomy, which give as many as 1300 for 2008.  Then, of course, we have Brian's Sky Notes to refer to.

At this point, Brian mentioned that it was important to know one's Personal Equation - reaction time between observing an event and pressing the stopwatch button.  It is something the observer is asked when submitting timings.  There are various Internet sites that allow you to measure it.  Brian said his was a slow 0.38 seconds.  I find that to be pretty reasonable...  I visited the BBC website where you can fire darts at sheep as they escape from their pen.  I would rather not talk about my own Personal Equation. Ed. 

We looked at three different kinds of event.

Observing the disappearance is the simplest, especially when the dark portion of the moon that occults the star has a faint amount of Earth Shine.  In the Occultation table in Brian's Sky Notes, DD denotes the Disappearance on the Dark limb and RD, the Reappearance on the Dark limb.  The star identification comes from the SAO catalogue, the Smithsonian Astrophysical Observatory star catalogue.

Fainter stars can sometimes be difficult to observe when the moon is nearer full and for this reason the PA angle - Position Angle - is given in the Sky Notes.  This is as seen with the naked eye.  It is measured from the moon's north pole in a counter-clockwise direction.  (Although telescopes can invert!)

This helps to predict the reappearance of the star from the dark limb, which can be as long as an hour after disappearance.

The timings are collated by central clearing houses, the main one being in Japan and are used for various purposes, such as refining knowledge of the moon's shape and motion, refining measurement of the Precession of the Earth's North Pole and the obliquity of the ecliptic (the Earth's axial tilt).

It is also possible to identify previously unknown double stars when the target disappears in two steps rather than one.

An exciting form of occultation is the Grazing Occultation, which involves observing a star as the moon's edge passes over it. 

It is important to be aware of the precise position the graze takes place on the Earth's surface.  A number of amateurs position themselves either side of the predicted line, which is very narrow indeed.  It can reveal mountains and valleys on the limb of the moon as the star disappears and reappears perhaps several times.

As an example of a grazing lunar occultation, Brian used one that happened near Tonbridge in 1979 where several observers were carefully placed along a road away from houses, obstructions, lights and noise.  The observer furthest north didn't see any occultation but this was regarded to be just as important as the other reports because it showed the limit of the occultation.

Grazing occultations help to refine the ecliptic latitude, refine the position of stars; something Brian had actually witnessed.

It is also feasible to measure the diameter of Supergiants and one gets more opportunities with a grazing occultation.

It is also possible to monitor the Earth's rotation rate.

For a grazing occultation, observers will need a stopwatch, an accurate source of time pulses such as an MSF receiver on 60 kHz and a tape recorder.  The tape recorder is very useful in recording events and then using the results by comparing them with a time source.

Brian's excellent talk showed how the work of the amateur astronomer still has an important place amongst the professional astronomers particularly in providing data from far more sources than fixed observatories allow.

JUNE MEETING

Wednesday 18th June 2008 Because this is one of the shortest nights of the year, in recent years the Society has held a members evening when we can bring telescopes, binoculars and other aids to amateur astronomy and chat about their use and discuss problems informally.  There will also be a short video on an astronomical subject.

The meeting begins at 1930 although members are invited to arrive anytime after 1900.  This is a good time to exchange ideas and discuss problems.

The venue as always is in the Upper Room of the Methodist Church at the east end of Wadhurst Lower High Street, opposite Uplands College.  (For those with SatNav -  the  Post code is TN5 6AX)

FUTURE MEETINGS & EVENTS  

Friday 20th June 2008  The Society's visit to see the Great Transit Circle at Greenwich Observatory.  

Wednesday 16th July 2008  There will be a talk given by James Fradgley called "Orbital Oddities - Strange Goings-on with 3 or more bodies" covering Lagrange Points, Resonances, Roche Limits, and lots of odds and ends with simulations.

James is a member of the Bournemouth Natural Science Society in Dorset.

Saturday 23rd August 2008  There is no Society meeting in August but Michael Harte and his wife Claire have very kindly invited the Society to an Astro-Barbecue.  This weekend is the late August Bank Holiday weekend and all members are invited.

In the past is has been a very enjoyable event and we usually take the occasional telescope and binoculars.  There is often the appearance of the latest gadget and members take great delight in trying them out.

Barbecue facilities are provided and we need to take just our own food and drink.

Michael suggests that members aim to arrive around 7.00 pm.

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  OTHER NEWS

 VISIT TO ROYAL OBSERVATORY GREENWICH

Friday 20th June 2008

Itinerary

10:15 Meet by the famous 24-hour clock just to the right of the main gate, below the Wolfe statue at the north end of Blackheath Avenue.  It is important to meet there and enter as a group.  Latecomers would need to find out where we were.

10:30 Start tour of Flamsteed House and the Octagon Room with a short stop for the Time Gallery.

Gilbert will then take us on a chronological tour of instruments starting with Flamsteed's (which are no longer in situ but Gilbert will show us where they went),  Halley's instruments and the developments up until the Airy instruments including the main Airy Transit Telescope which Gilbert himself used to use. The breadth of this display is apparently unique in the world.

Gilbert will then briefly show us the 28" Refractor in the main dome.

We then pass through the shop on our way to lunch.

12:30 Break for lunch.  There is a café in the south building and also the Tea House Pavilion in the park or members may prefer to take a packed lunch.

In the afternoon we would be on our own and have free time to go back to the Time Galleries or go to the Old Planetarium in the South Building where there is a large exhibition on Space which can take quite a while to go around at our own pace.

After this we could then meet up and have a group visit to the New Peter Harrison Planetarium (accessed through the Old Planetarium South Building), which will be a bit cheaper for entrance if we are still in sufficient numbers.

There are different shows during the day, these are:

Black Holes: The other side of Infinity.

Weekdays 13:00, and 15:00

In this spectacular new show, discover the early universe, witness star birth and death and the collision of galaxies and fly into a massive black hole lurking at the heart of the Milky Way. Narrated by Liam Neeson.

Sky Tonight Live.

Weekdays 16:00

Presented live by a Royal Observatory astronomer, you will be taken on a tour of what you can see for yourself in tonight's night sky.

Star Life.

Daily: 14.00

This visually-stunning show looks at the lives of stars - how they are born, grow up, grow old and die; how black-holes and pulsars form and how beautiful clouds of glowing gas come into existence. Hosted by real astronomers who are available to answer questions after the main programme.

Gilbert thought that the "Sky Tonight Live" was good as it was presented live by an astronomer. It is at 16:00.  It would be a fitting conclusion to our visit.  Phil has taken a note of those members who have indicated that they would be interested in going to this presentation and if there are enough numbers he may see if it is possible to obtain a group ticket.  It might make a slight saving.

The only charge is the entrance to the planetarium.  £6.00 per individual adult.

Members need to make their own transport arrangements as we did for last year's visit to Belmont House.

Phil Berry visited Greenwich Park recently and noted that Car Parking was mainly along Blackheath Avenue, which is the long avenue inside Greenwich Park when approaching from the main gate from Blackheath and ends at the Wolfe Statue.

Parking is charged at £1 an hour with a maximum of four hours.  To park after this time, it will be necessary to move to another meter.  One cannot park again at the same meter that day.

THE "HELP LIST"

The "Help List" on a clipboard is available at each meeting and is for members to use when asking for help or information.  This is a useful way of introducing problems being experienced and queries by members.

SKY NOTES FOR JUNE 

Planets

Mercury is not suitably placed for observation this month following inferior conjunction (passing in between the Earth and Sun) on the 7th.

Venus is also not visible this month having passed through superior conjunction (passing literally in this case behind the Sun as seen from the Earth) on the 9th.

Mars at magnitude +1.6 (and still fading) is moving eastward and crosses the border from Cancer (the crab) into Leo (the lion) during June on its way to a rendezvous with Saturn next month. Mars sets just after midnight (BST) by the middle of the month.

Jupiter lies in the constellation of Sagittarius (the archer) at a magnitude of -2.7. By the middle of June it rises before 23.00 (BST) and is a striking object although quite low down.

Saturn is still in Leo at magnitude +0.8 and is close to the bright star Regulus (a Leonis). Saturn sets around midnight (BST) by the end of the month.

Lunar Occultations

As usual I've only included events for stars down to around magnitude 7.5 that occur before midnight BST. As you can see, there are events on 6th and 14th where the star disappears and reappears (both on the dark limb) within a short space of time. If we were to travel 27 miles to the north on June 6th we would be able to see a graze occultation of SAO 79909.

Phases of the Moon for June

ISS

Brian Mills

NASA SPACE PLACE

Ozone, the Greenhouse Gas

We all know that ozone in the stratosphere blocks harmful ultraviolet sunlight, and perhaps some people know that ozone at the Earth's surface is itself harmful, damaging people's lungs and contributing to smog.

But did you know that ozone also acts as a potent greenhouse gas? At middle altitudes between the ground and the stratosphere, ozone captures heat much as carbon dioxide does.

In fact, pound for pound, ozone is about 3000 times stronger as a greenhouse gas than CO2. So even though there's much less ozone at middle altitudes than CO2, it still packs a considerable punch.  Ozone traps up to one-third as much heat as the better known culprit in climate change.

Scientists now have an unprecedented view of this mid-altitude ozone thanks to an instrument aboard NASA's Aura satellite called the Tropospheric Emission Spectrometer-"TES" for short.

Most satellites can measure only the total amount of ozone in a vertical column of air. They can't distinguish between helpful ozone in the stratosphere, harmful ozone at the ground, and heat-trapping ozone in between.  By looking sideways toward Earth's horizon, a few satellites have managed to probe the vertical distribution of ozone, but only to the bottom of the stratosphere.

Unlike the others, TES can measure the distribution of ozone all the way down to the heat-trapping middle altitudes. "We see vertical information in ozone that nobody else has measured before from space," says Annmarie Eldering, Deputy Principal Investigator for TES.

The global perspective offered by an orbiting satellite is especially important for ozone. Ozone is highly reactive. It is constantly being created and destroyed by photochemical reactions in the atmosphere and by lightning. So its concentration varies from region to region, from season to season, and as the wind blows.

Data from TES show that ozone's heat-trapping effect is greatest in the spring, when intensifying sunlight and warming temperatures fuel the reactions that generate ozone. Most of ozone's contribution to the greenhouse effect occurs within 45 degrees latitude from the equator.

Increasing industrialization, particularly in the developing world, could lead to an increase in mid-altitude ozone, Eldering says. Cars and coal-fired power plants release air pollutants that later react to produce more ozone.

"There's concern that overall background levels are slowly increasing over time," Eldering says. TES will continue to monitor these trends, she says, keeping a careful eye on ozone, the greenhouse gas.

Learn more about TES and the science of ozone at: tes.jpl.nasa.gov/

Kids can get a great introduction to good ozone and bad ozone at: spaceplace.nasa.gov/en/kids/tes/gases

This article was provided by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.

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CONTACTS

Chairman   John Vale-Taylor 

Phil Berry  01892 783544

Treasurer  Mike Wyles  01892 542863

Publicity & Website  Michael Harte  01892 783292

Newsletter Editor  Geoff Rathbone  01959 524727

Any material for inclusion in the July 2008 Newsletter should be with the Editor by June 28th  2008

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